The present invention relates to a method of measuring metallic impurities contained within a fluid and an apparatus for subjecting such a fluid to an X-ray fluorescence analysis to conduct the measurement. More particularly, the present invention relates to such a method and apparatus in which both solid and vapor phases of the metallic impurities are adsorbed in microporous filter and such filter is subjected to the on-line analysis.
Metallic impurities gases used in the fabrication of semiconductor devices can have major deleterious effects on semiconductor production. Such impurities arise because gases and liquids used within the fabrication of semiconductors are extremely corrosive. Examples of such gases are hydrogen chloride, hydrogen bromide, boron trichloride, tungsten hexaflouride and chlorine. Liquids include hydrogen bromide, hydrogen chloride, boron trichloride and chlorine. In any event, such corrosive special gases when passing through distribution systems such as tubing and chambers react with metal to produce such metallic impurities as FeCl.sub.3, ZrCl.sub.4, HgCl.sub.2, and MoF.sub.6 and UF.sub.6. All of such impurities have a vapor pressure as high as about 1 Torr below 200.degree. C. so that in the course of semiconductor fabrication, such impurities will exist in both solid and vapor forms. Thus, there exists the need to continually monitor a gas distribution system or the output of a cylinder containing such a corrosive special gas.
The prior art has recognized the monitoring requirement in U.S. Pat. No. 5,618,996. In this patent, a fluid sample stream is passed through two membrane filters situated in series. The first filter is maintained at room temperature to adsorb the particle impurities. The second filter is maintained at cryogenic temperatures to freeze out the vapor phase of the impurities. After sampling is completed, the sampling apparatus is disconnected from the facility at which the measurements are to be conducted and transported to an analysis location where analysis can be completed by ICPMS (Inductively Coupled Plasma Mass Spectrometer). As can be appreciated, the method and device of this patent can not be used to continuously sample the feed and to measure metallic impurities on-line. Moreover, a cryogenic liquid, such as liquid carbon dioxide must be on hand in order for the equipment to perform its sampling function.
As will be discussed, the present invention provides a method and apparatus that can be used to sample a stream for particulate and vapor phases of metallic impurities on a continuous basis and without the requirement of providing cryogenic fluids.